1. Field of the Invention
The present invention relates to a gas turbine control apparatus by which combustion fluctuation is controlled to be suppressed and also relates to a gas turbine system using the gas turbine control apparatus and a gas turbine control method based on the same concept.
2. Description of the Prior Art
In a prior art gas turbine, flow rates of air and fuel to be supplied into a combustor are decided in advance based on a generator output, atmospheric temperature and humidity, etc. and by using the values thereof, operation of the gas turbine is carried out. However, due to aged deterioration, such as deterioration of a compressor performance, clogging of a filter, or the like, there is a possibility that the actual flow rates of fuel and air deviate from planned values or adjusted values of the trial operation time. In this case, there is a possibility that the combustion stability is deteriorated or combustion fluctuation arises. If combustion fluctuation arises, operation of the gas turbine may be largely obstructed. That is, from the viewpoint of preservation of the plant facilities and enhancement of the availability of the plant, to suppress and avoid the combustion fluctuation to the extent possible is strongly desired. Thus, in order to maintain the combustion stability and avoid the combustion fluctuation, adjustments of the control system are carried out several times a year by skilled operators so that the combustion stability is confirmed and maintained and this invites an increase of the maintenance cost and a deterioration of the availability.
Patent Document 1 (the Japanese laid-open patent application 1997-269107) discloses a combustion fluctuation suppressing device of a combustor and a method thereof.
This combustion fluctuation suppressing device of a combustor comprises a combustion fluctuation suppressing portion. This combustion fluctuation suppressing portion comprises a frequency analyzing device performing a frequency analysis of pressure fluctuation of combustion gas detected by a pressure sensor in the combustor, a central computing and processing unit processing a fluctuation stability based on frequency bands of the pressure fluctuation analyzed by the frequency analyzing device, a voltage amplifier amplifying an output signal of the central computing and processing unit and a controlling portion performing a control by giving the amplified output signal as a valve opening and closing signal into a fuel valve.
This fluctuation suppressing method puts eyes on the low frequency combustion fluctuation. That is, based on a fuel-air ratio at the time of occurrence of the combustion fluctuation, the frequency of the combustion fluctuation is predicted. In case of the low frequency combustion fluctuation, by changing the fuel-air ratio, occurrence of the low frequency combustion fluctuation can be suppressed. As the low frequency combustion fluctuation is liable to give influences on the machine parts and components, by suppressing the low frequency combustion fluctuation, damages of the machine parts and components are suppressed.
However, the combustion fluctuation suppressing method of the Patent Document 1 relates to the low frequency combustion fluctuation, as mentioned above. Actually, the combustion fluctuation arising in the gas turbine can be caused in a wide range of frequency bands from a low frequency to a high frequency of several thousands Hz for various reasons. Moreover, the combustion fluctuation may arise simultaneously in a plurality of frequency bands. If the fuel-air ratio is changed based on the combustion fluctuation of the low frequency band only, there may be a bad influence on the combustion fluctuation of other frequency bands.
In this way, by simply suppressing the combustion fluctuation only of the low frequency, it is difficult to effectively realize a stability of the combustion.
By the way, the combustion fluctuation suppressing means is usually such one as to carry out the control so as to avoid the combustion fluctuation just after the combustion fluctuation has arisen. Hence, even if a steady operation having no combustion fluctuation is being carried out, as various combustion fluctuation suppressing means are used therein, such steady state may include a state of the boundary that the combustion fluctuation almost arises.
Also, corresponding to the change in the air temperature or humitity due to the seasonal variation or corresponding to the deterioration or deformation of each of the gas turbine parts and components due to aged deterioration, etc., even if the outside condition, such as the air temperature or humidity, is the same, the combustion state does not always become the same.
Moreover, such a state that a steady operation without the combustion fluctuation is carried out may not always be the best from the economical point of view, etc. For example, in Patent Document 2 (the Japanese laid-open patent application 2003-232230), in order to suppress emissions of nitrogen oxides discharged from a combustor to a target level, to control fuel to be supplied into each of plural combustors is carried out. In this way, it is preferable to carry out the control of the gas turbine operation based on the conditions balanced from various points of view including not only suppressing the combustion fluctuation but also suppressing the emissions, etc.
In the present situation, however, in the control of the gas turbine operation, there is still a large room for enhancing the stability, economy of operation, environment preservation performance, etc.